There are various entrances for MBA you can give to get into the right bschool for you.
Some of the entrances are:

CAT< XAT< MAT< NMAT< CMAT etc..

You need minimum 50% to be eligible to give MBA entrances.
CAT applications have been started. Fill the form from here: CAT APPLICATION FORM

You can check the step by step application process from here:
CAT application filling process

Also you can check the complete notification for MBA exams below:

MBA Exams notifications

Keep a track for dates and registrations.

Good luck!